Question

how many 3 digit numbers can be formed by using only two digits 1 and 2?​

Answer 1

hey we can make many numbers like

Step-by-step explanation:

112 ,111 ,222 ,221

Answer 2

Easy

Consider this problem as filling 3 blank spaces using 3 digits where repitions of digits are not allowed . Now lets talk about the 3 spaces in pointwise manner.

The first blank space can be filled using 1 or 2 or 3 which leaves us with 3 ways of doing this tasks , Hence the first space can be filled in 3 ways.

The Second Blank Space can be filled only in 2 ways as our choices gets reduced after filling first space,Since repititions are not allowed, Example if we filled first space with number 3 then second space can be filled using 1 or 2 only as repititions are not allowed. Hence second space can be filled in 2 ways.

On similar lines we can argue that last space can be filled in 1 way.

Now as filling of all these spaces is an independent tasks , Hence By Product Rule we have.

Total Number of ways= 3*2*1=6 ways.

Thanks for reading :) .